1. Field of the Invention
The present invention relates to an apparatus for manufacturing a semiconductor single crystal in a hydrogen-containing atmosphere.
This application claims priority from Japanese Patent Application No. 2005-180001, filed on Jun. 20, 2005, and U.S. Provisional Patent Application No. 60/693,945, filed on Jun. 27, 2005, the contents of which are incorporated herein by reference.
2. Background Art
A silicon single crystal, which is one type of semiconductor single crystal, is manufactured by using a heater to heat a polycrystalline silicon starting material held in a crucible within an airtight chamber so as to form a silicon melt, and growing a silicon single crystal while pulling it from the silicon melt by the Czochralski (CZ) method. The resulting silicon ingot is sliced to prepare silicon wafers, and chips such as integrated circuits are fabricated on the silicon wafers.
An inert gas (primarily argon gas) has hitherto been used as the atmosphere within the chamber when pulling such a silicon single crystal. The reason for using the inert gas is to inhibit chemical reactions between the silicon melt, components of the chamber and the growing silicon ingot, thereby avoiding entry of byproduct-forming impurities. In addition, when supplying a large amount of gas, a flow of gas within the chamber arises. By utilizing the flow of gas within the chamber, metal contamination can be avoided, enabling a silicon single crystal of higher quality to be achieved.
The effectiveness of admixing a very small amount of hydrogen gas in the atmosphere within such a chamber has recently began to be reported (see, for example, Patent Documents 1 to 4). According to the art disclosed in these Patent Documents, the hydrogen atoms act upon grown-in defects, particularly void defects such as crystal oriented particles (COP), that have been introduced into the crystal, thereby being able to shrink or eliminate void defects in much the same way as nitrogen doping of the silicon melt.
Known techniques for safely supplying hydrogen gas, which is flammable, into such a chamber include a method for specifying a hydrogen concentration using a triangular diagram (Patent Document 5), and a method for supplying hydrogen gas so as to efficiently dissolve hydrogen atoms into a silicon melt (Patent Document 6).
However, the prior-art method for supplying hydrogen gas into a chamber described in Patent Document 6 is a method for supplying hydrogen mixed gas which uses a hydrogen gas supplying device that stores beforehand in a cylinder or the like an amount of hydrogen mixed gas required for at least one pull of a silicon single crystal in a hydrogen atmosphere. In such a prior-art method for supplying hydrogen mixed gas, because a content of hydrogen atoms in the hydrogen mixed gas is predetermined, it is very difficult to optimally control the hydrogen concentration in response to changes in a crystal pulling environment during pulling of the silicon single crystal. Hence, achieving maximum benefits of pulling a silicon single crystal in a hydrogen atmosphere is a challenge.
Also, because an apparatus for manufacturing a silicon single crystal having a large diameter that uses several hundred liters or more per minute of such a hydrogen mixed gas would require a hydrogen mixed gas storage means of a quite considerable size, there is some concern that such a prior-art arrangement would entail high equipment costs. An additional concern is the difficulty of continuously and stably supplying hydrogen mixed gas into the chamber at a high flow rate over a period of several days during a single pull.
Patent Document 1: Japanese Unexamined Patent Application, First Publication No. S61-178495
Patent Document 2: Japanese Unexamined Patent Application, First Publication No. H11-189495
Patent Document 3: Japanese Unexamined Patent Application, First Publication No. 2000-281491
Patent Document 4: Japanese Unexamined Patent Application, First Publication No. 2001-335396
Patent Document 5: Japanese Unexamined Patent Application, First Publication No. 2004-182525
Patent Document 6: Japanese Unexamined Patent Application, First Publication No. 2004-217460